Field of the Invention
The present invention relates to GH61 polypeptide variants, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
Description of the Related Art
Cellulose is a polymer of the simple sugar glucose covalently linked by beta-1,4-bonds. Many microorganisms produce enzymes that hydrolyze beta-linked glucans. These enzymes include endoglucanases, cellobiohydrolases, and beta-glucosidases. Endoglucanases digest the cellulose polymer at random locations, opening it to attack by cellobiohydrolases. Cellobiohydrolases sequentially release molecules of cellobiose from the ends of the cellulose polymer. Cellobiose is a water-soluble beta-1,4-linked dimer of glucose. Beta-glucosidases hydrolyze cellobiose to glucose.
The conversion of lignocellulosic feedstocks into ethanol has the advantages of the ready availability of large amounts of feedstock, the desirability of avoiding burning or land filling the materials, and the cleanliness of the ethanol fuel. Wood, agricultural residues, herbaceous crops, and municipal solid wastes have been considered as feedstocks for ethanol production. These materials primarily consist of cellulose, hemicellulose, and lignin. Once the lignocellulose is converted to fermentable sugars, e.g., glucose, the fermentable sugars can easily be fermented by yeast into ethanol.
WO 2005/074647, WO 2008/148131, and WO 2011/035027 disclose isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Thielavia terrestris. WO 2005/074656 and WO 2010/065830 disclose isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Thermoascus aurantiacus. WO 2007/089290 and WO 2012/149344 disclose isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Trichoderma reesei. WO 2009/085935, WO 2009/085859, WO 2009/085864, and WO 2009/085868 disclose isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Myceliophthora thermophila. WO 2010/138754 discloses an isolated GH61 polypeptide having cellulolytic enhancing activity and the polynucleotide thereof from Aspergillus fumigatus. WO 2011/005867 discloses an isolated GH61 polypeptide having cellulolytic enhancing activity and the polynucleotide thereof from Penicillium pinophilum. WO 2011/039319 discloses an isolated GH61 polypeptide having cellulolytic enhancing activity and the polynucleotide thereof from Thermoascus sp. WO 2011/041397 discloses an isolated GH61 polypeptide having cellulolytic enhancing activity and the polynucleotide thereof from Penicillium sp. WO 2011/041504 discloses isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Thermoascus crustaceus. WO 2012/030799 discloses isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Aspergillus aculeatus. WO 2012/113340 discloses isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Thermomyces lanuginosus. WO 2012/122477 discloses isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Aurantiporus alborubescens, Trichophaea saccata, and Penicillium thomii. WO 2012/135659 discloses an isolated GH61 polypeptide having cellulolytic enhancing activity and the polynucleotide thereof from Talaromyces stipitatus. WO 2012/146171 discloses isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Humicola insolens. WO 2012/101206 discloses isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Malbranchea cinnamomea, Talaromyces leycettanus, and Chaetomium thermophilum. WO 2013/043910 discloses isolated GH61 polypeptides having cellulolytic enhancing activity and the polynucleotides thereof from Acrophialophora fusispora and Corynascus sepedonium. 
WO 2012/044835 and WO 2012/044836 disclose GH61 polypeptide variants having cellulolytic enhancing activity with improved thermal activity and thermostability.
There is a need in the art for GH61 polypeptides having cellulolytic enhancing activity with increased thermostability as a component of enzyme compositions for use in the degradation of lignocellulose at high temperatures.
The present invention provides GH61 polypeptide variants with increased thermostability.